1. Field of the Invention
This invention relates to the oxo process, particularly to the catalyst cycle. That is, it relates to an improved process for removing metal-containing catalyst residues, especially of metals of Group VIII of the Periodic Table, e.g., cobalt, from crude oxo reaction products, to purify the latter, and recovering such catalyst residues in a form suitable for recycle to the oxo reaction. Thus, the present invention concerns a fully integrated demetalling-catalyst recovery process wherein obtaining the catalyst in suitable form for recycling is achieved.
The oxo process is well known and involves the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen (synthesis gas) with carbon compounds containing olefinic linkages in the presence of a carbonylation catalyst at hydroformylation conditions which include synthesis gas pressures of 1500 to 4500 psig and temperatures in the range of 150.degree.-450.degree. F.
This carbonylation reaction provides a particularly attractive method for preparing valuable primary alcohols which find large markets, particularly as intermediates for plasticizers, detergents and solvents. Amenable to the reaction are long and short chained olefinic compounds, depending upon the type alcohols desired. Not only olefins, but most organic compounds possessing at least one non-aromatic carbon-carbon double bond may be reacted by this method. Thus, straight and branch-chained olefins and diolefins such as propylene, butylene, pentene, hexene, heptene, butadiene, pentadiene, styrene, olefin polymers such as di- and tri-isobutylene and hexene and heptene dimers, polypropylene, olefinic fractions from the hydrocarbon synthesis process, steam cracking or catalytic cracking operations, and other sources of hydrocarbon fractions containing olefins may be used as starting material, depending upon the nature of the final product desired.
Chief among the catalysts used has been a metallic soap, viz, cobalt oleate. However, there has been continued interest in other, lower cost alternatives to the expensive cobalt soap, which, during use, is converted to other forms that have to be reconverted to the soap.
Regardless of the catalyst used, during the process the oxo products obtained are contaminated with metal-containing catalyst residues which must be removed in order to obtain purified materials, e.g., aldehydes and, subsequently, after hydrogenation, alcohols. Because of the strategic importance and the increasing cost of cobalt, it is desirable that substantially all of the metal be recovered and reutilized.
2. Description of the Prior Art
U.S. Pat. No. 2,751,403 issued on June 19, 1956 to J. K. Mertzweiller discloses that the cobalt in a contaminated crude aldehyde oxo product can be removed by extraction with an aqueous acid such as acetic acid and that the aqueous extract will contain cobalt in both the cationic and anionic forms, viz., as the anion [Co(CO).sub.4 ].sup.- and the corresponding cobalt salt, cobalt bis cobalttetracarbonylate, Co.sup.++ [Co(CO).sub.4 .sup.-.sub.2. The patentee subjected the aqueous extract to oxidation with the addition of, e.g., sodium oleate, to convert anionic cobalt to cobaltous ion and yield cobalt oleate, which was the desired catalytic species. U.S. Pat. No. 2,757,377 issued on July 31, 1956 to J. K. Mertzweiller et al. is similarly directed to elimination of anionic cobalt. The process involves thermal degassing of the aldehyde feed prior to the acid decobalting operation and recovering an aqueous solution of cobaltous ion which can be readily converted to the soap.
In U.S. Pat. No. 2,757,205 issued on July 31, 1956 to J. K. Mertzweiller et al., the aqueous solution containing Co[Co(CO).sub.4 ].sub.2 recovered from the catalyst removal zone is passed to the carbonylation zone to supply "at least a portion" of the catalytic requirements thereof. In U.S. Pat. No. 2,744,936 issued on May 8, 1956 to J. K. Mertzweiller, decobalting is carried out by means of an aqueous solution that provides cobaltous ions, e.g., cobalt acetate, which reacts with [Co(CO).sub.4 ].sup.- ions present to give Co[Co(CO).sub.4 ].sub.2, the latter being passed to the carbonylation zone as catalyst.
The catalyst species is considered to be a form of the hydrido cobalt tetracarbonyl, HCo(CO).sub.4, in equilibrium with hydridocobalt tricarbonyl, HCo(CO).sub.3, according to "Organic Syntheses via Metal Carbonyls," Wender and Pino, Interscience Publishers, Volume 1, pp. 249-251.
DT-AS No. 2,244,373 to Badische Anilin & Soda-Fabrik Akt. filed on Sept. 9, 1972, describes a process which consists essentially of:
(a) demetalling the crude oxo product with an aqueous solution of an organic or an inorganic acid and oxygen to obtain the aqueous solution of a cobalt salt, e.g., cobalt acetate, formate, butyrate, chloride or nitrate; PA1 (b) contacting the aqueous solution of the cobalt salt formed in step (a) with an organic solvent, e.g., alcohols or aldehydes, which solvent contains cobalt carbonyls, in the presence of synthesis gas at a pressure in the range of 50 to 500 atmospheres and at a temperature ranging from 50.degree. C. to 500.degree. C., in order to convert the water-soluble cobalt salt to hydridocobalttetracarbonyl; and, thereafter, PA1 (c) continuously recycling the organic solvent, which contains cobalt carbonyls, in a closed loop to step (b) in order to continuously convert the aqueous cobalt salt to hydridocobalttetracarbonyl, the aqueous phase containing the latter and gas phase in which it may be present, constituting the recovered catalyst.
As can be seen from the steps outlined above, characteristic features of the BASF process are that it initially obtains the catalyst residues from the oxo product entirely as the inactive Co.sup.++ salt and continuously recycles an organic solvent in which a content of Co.sup.- has been build up to trigger the autocatalytic conversion of Co.sup.++ to Co.sup.-1 in a separate preforming step (b). Thus there is no conservation of the active form of cobalt present in the metal-containing crude oxo product, whereas this is achieved by means of the subject invention.
An important distinction over this reference is that the patentee starts from a condition of zero content of cobalt carbonyls and must first preform 100% of the amount needed as catalyst to get the preforming reaction going, which is more difficult than if some were already present; whereas in the present process cobalt carbonyls extracted from the oxo products and preserved are available so that the preforming reaction is ready to convert only that Co.sup.++ which is present in excess of the Co.sup.++ in Co.sup.++ [Co.sup.- (CO).sub.4 ].sub.2.
U.S. Pat. No. 3,941,848 issued on Mar. 2, 1976, also assigned to BASF, has the same disadvantage described above. In addition it employs a heterogeneous catalyst for the preforming step such as activated carbon, zeolites and ion exchange resins impregnated with cobalt carbonyls whereas the present process utilizes a water soluble cobalt carbonyl compound as homogeneous catalyst for that purpose.